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PEPFAR Quality Control and Method Validation Activity 14 Handout: Reference Interval

This PDF contains supportive documents for Activity 14.

190 Reference Interval Handout 14D02 Chemistry Reference Interval Guidelines I. The REFERENCE INTERVAL (OR REFERENCE RANGE) is the range of test values expected for a designated population in which 95% of the individuals are presumed to be healthy (or normal). When transferring or verifying a reference interval, ensure the comparability of the test subject population. If there are substantial differences in the geographic locations or demographic variables of the two populations that are known to cause differences in the reference values, then a reference interval must be established. II. Transference of Reference Ranges with Verification A. Select reference range to be verified. 1. Current laboratory ranges 2. Manufacturer's r anges 3. Published reference ranges 4. Locally established reference ranges B. Determine population to be used to verify reference range. 1. Qualify healthy volunteers --this can be done through a questionnaire or health assessment. (See Appendix 1 Sample Health Questionnaire.) 2. Obtain samples from 20 healthy participants for each range to be verified. 3. Test each sample immediately and evaluate. C. If Then 2 90% of samples are The reference range is within the reference verified. range < 90% of samples are Re-evaluate the range being within the reference verified. range Re-evaluate the healthy volunteer qualifications. Collect and evaluate 20 additional samples. 90% of the additional The reference range is IV samples are within the verified. reference range < 90% of the additional Proceed with step III below samples are within the (Establishment of Reference reference range Ranges) Modified from pSMILE.org website. Equ35-A-07_Ref_Rng_Rqmt_Chem. Last accessed May 3, 2013 HILS1746 Page 1 of 4 Effective Date: 12/6/2016 191 Reference Interval Handout 14D02 III. Establishment of Reference Ranges A. Determine population to be used to establish reference range. 1. Qualify healthy volunteers. This can be done through a questionnaire or health assessment. (See Appendix 1 Sample Health Questionnaire.) 2. Obtain samples from 120 healthy participants for each range to be verified. The 40 samples previously collected in step I above can be used as part of the 120 samples. 3. Test each sample immediately after collection and evaluate. It is not advisable to collect and test all samples on the same day. B. Evaluation of data 1. Plot the data in a histogram and visually evaluate the frequency distribution and outliers. 2. Eliminate outliers based on visual examination and clinical experience. 3. Use a non-parametric method to determine the reference range. a. Rank (order by size) the values from lowest to highest. Example: Female Calcium Results (mg/dL) (Data from samples 6 - 115 omitted for example purposes) Sample 1 8.8 Sample 116 10.1 Sample 2 8.9 Sample 117 10.1 Sample 3 8.9 Sample 118 10.2 Sample 4 8.10 Sample 119 10.3 Sample 5 8.11 Sample 120 10.4 b. Multiply the total number of samples +1 by 0.025 to determine the sample number that represents the low end of the range. Example: Total number of samples= 120. Low end = (120 + 1) x 0.025 = 3.025 = 3. Sample 3 is the low end: 8.9 mg/dL. c. Multiply the total number of samples +1 by 0.975 to determine the sample number that represents the high end of the range. Example: Total number of samples= 120. High end = (120 + 1) x 0.975 = 117.975 = 118. Sample 118 is the high end: 10.2 mg/dL d. Use these rank values to estimate the upper and lower reference limits. Example: Reference range is "Sample 3 to Sample 118" or 8.9 - 10.2 mg/dL Modified from pSMILE.org website. Equ35-A-07_Ref_Rng_Rqmt_Chem. Last accessed May 3, 2013 HILS1746 Page 2 of 4 Effective Date: 12/6/2016 192 Reference Interval Handout 14D02 IV. Transference of Reference Ranges without Verification The CLSI C28-A2 describes different ways for a laboratory to validate the "transference" of established reference intervals. Pediatric reference intervals often require this approach because of the difficulty in obtaining sufficient specimens to establish or verify reference intervals. If a laboratory wishes to transfer a reference interval established by another laboratory or publication, the acceptability should be assessed based on several factors: A. Similarity of geographics and demographics. B. Similarity of test methodology. C. Sound clinical judgment and consultation with local medical professionals. D. Approval by the laboratory medical director is required and must be documented. V. References A. GCLP Workshop and Workbook18-20 May 2008, Verification of Performance Specifications, pages 1-33. B. Clinical and Laboratory Standards Institute (CLSI). Defining, Establishing, and Verifying Reference Intervals in the Clinical Laboratory Proposed Guideline-Third Edition, March 2008. CLSI document C28-A3c (ISBN 1-56238-682-4). Clinical and Laboratory Standards Institutes, 940 West Valley Road, Suite 100, Wayne, Pennsylvania 19098-1898 USA, 2005. C. Westgard, James O. (2003). Basic Method Validation (2nd ed.). Madison: Westgard QC, Inc. D. Westgard, James O. (2008). Basic Method Validation (3rd ed.). Madison: Westgard QC, Inc. Modified from pSMILE.org website. Equ35-A-07_Ref_Rng_Rqmt_Chem. Last accessed May 3, 2013 HILS1746 Page 3 of 4 Effective Date: 12/6/2016 193 Reference Interval Handout 14D02 Annex 1: Sample Health Questionnaire General Health Questionnaire for Donors for Verification of Reference Range Study Date: Place of Session: Sample Number: (also record below) Surname: First Name: Middle Name: Sex:__ Date of Birth: Contact Address: Telephone: I understand that my blood will be tested for INSERT NAME(S) OF TEST(S) Phlebotomist's Name: Signature of Donor: Y N Have you had any unexplained fever in the past 3 months? Have you lost more than 10% body weight in the past 6 months? Have had jaundice in the past 12 months? Have you ever had a blood transfusion? Have you ever had an operation? Are you on any medication? Ladies, are you pregnant, lactating or menstruating? Is this potential donor in good health? Y / N Phlebotomist Name: Phlebotomist Signature: Sample Number: (from above) Modified from pSMILE.org website. Equ35-A-07_Ref_Rng_Rqmt_Chem. Last accessed May 3, 2013 HILS1746 Page 4 of 4 Effective Date: 12/6/2016